This paper studies the diffraction in the near-field of a monochromatic Gaussian beam by a sequence of parallel coaxial
circular apertures. A method to design diffraction-based and wavelength-specific focusing systems through a sequence of
circular apertures, using confocal Fresnel ellipsoids, is detailed. The results obtained with this research show that the design
method introduced here is valid and can be used to focus electromagnetic beams without traditional refractive lenses.